Cutting instrument and methods for implementing same

ABSTRACT

A rotating cutting tool ( 10, 110 ) includes a body ( 12, 112 ) with a longitudinal axis ( 14, 114 ) and at least one flute ( 16, 116 ) and one active part ( 18, 118 ). Each active part has a peripheral surface including: a radial cutting edge ( 20, 120 ) that is at a cutting distance (Rc) from the longitudinal axis, a clearance face ( 30, 130 ) that is at a final clearance distance (Rd) from the longitudinal axis, and a control face ( 40, 140 ) that is at a penetration control distance (Rp) from the longitudinal axis. These distances satisfy the relation: 
         0&lt;Δ   p&lt;Δd , with Δ p=|Rc−Rp | and Δ d=|Rc−Rd|.

The present invention relates to the field of cutting tools. It is aimedmore particularly at a rotating cutting tool such as a milling cutter ordrill. It is aimed as well at methods implementing such a cutting tool.

In the following outline, the term of “milling cutter” is used in thewidest sense. It extends to borers as well as to the annular cuttersthat turn around a workpiece. In the following outline, such an annularcutter is called a “shell-type milling cutter”, and a nonannular cutteris called a “solid-type milling cutter”. In the following outline, theterm of “longitudinal” refers to an entity substantially parallel to alongitudinal axis, while the term of “transverse” refers to an entitysubstantially perpendicular to this longitudinal axis.

A cutting tool according to the invention finds applications in numerousfields. A solid-type milling cutter can be used in the medical field,particularly in the dental field for endodontic treatments when boringroot canals, shaping stumps, preparing and cutting crowns, and preparingcavities. A shell-type milling cutter can be used in the field ofjewelery, for instance for the machining of setting claws. Thoughfavoured, these applications are not limiting for the cutting toolaccording to the invention.

The dental field and the field of jewelery have in common that theelements to be machined or shaped—teeth or setting claws—have smalldimensions and require a great precision of the machining operations.They have in common, too, that the technologies implemented forrealising the cutting tools are similar.

The shaping of the cavities, false preprosthetic stumps, and prosthesesis realised with milling cutters having highly varied geometries. Thesecutters can be round, cylindrical with a round end or a flat end,conical, ogival, etc. These cutters can have different diameters rangingfrom 0.6 mm to several millimeters. These cutters have several teeth,generally six. They have a cutting capacity that depends on theirgeometry.

An extended time of working with the cutting tool may lead to heating ofthe tool and of the material being machined, that is, of the dentine orprosthetic material. It will then be necessary to plan breaks forcooling that translate into a loss of time for the practician andreduced comfort for the patient being treated. An extended time ofworking may also lead to important wear of the cutting tool.

In the field of jewelery, the conditions of use are more particularlytied to the dimensions of the pieces being machined, and to the qualitydesired for the surfaces obtained after machining.

One already knows milling cutters of the solid type that are used in thedental field, and milling cutters of the shell type that are used in thefield of jewelery.

These cutting tools exhibit an alternation of active parts and flutes.Every active part includes at least one radial cutting edge that attacksthe material to be machined in a more or less aggressive way, generatingchips of material removed. The chips are eliminated through a fluteadjacent to the radial cutting edge.

It sometimes happens that the chips are not completely eliminatedthrough the flutes, and get between the active part of the cutting tooland the material to be machined. These chips remain more or less mobile,or else aggregate in a particular region. In the field of endodontywhere solid-type milling cutters are applied, chips get between theactive part of the cutting tool and the wall of the root canal beingcleaned, and may become lodged in recesses of the root canal. In thefield of jewelery, where shell-type milling cutters are applied, thechips get between the active part of the cutting tool and the outersurface of the setting claw, and may remain mobile between these twoparts. Chips not eliminated will in all cases perturb the machiningoperation. They may block the cutting tool or cause it to skid.

It is not always easy, moreover, to know at all times the true impact ofthe cutting tool on the material to be machined, and to proportion thepower of the cutting tool, be it on the walls of teeth with a solid-typemilling cutter or on the outside of a setting claw with a shell-typemilling cutter.

It is one aim of the present invention to propose a cutting tool of therotating type that could be used in particular in the dental field oranother medical field, as well as in the field of jewelery, withoutbeing limited to that, and that overcomes the disadvantages mentionedhereinabove.

According to a first aspect, the invention refers to a cutting tool ofthe rotating type, and in particular a milling cutter or borer, saidcutting tool being provided with a body having a longitudinal axis andat least one flute alternating with at least one active part. Accordingto the invention, every active part has a peripheral surface comprisingin succession:

-   -   a radial cutting edge,    -   a clearance face to favour elimination of the chips, and    -   a control face to control the depth of penetration of the        cutting, said control face opening into a flute,

and

-   -   said radial cutting edge defines a cutting envelope and is        situated at a cutting distance Rc from said longitudinal axis,    -   said clearance face is defined by an angular clearance length        and is situated at a distance from said longitudinal axis that        varies between the cutting distance Rc and a final clearance        distance Rd,    -   said control face is defined by an angular penetration control        length and is situated at a penetration control distance Rp from        said longitudinal axis, and    -   the absolute difference Δp between said cutting distance Rc and        said penetration control distance Rp is larger than zero, and        smaller than the absolute difference Δd between said cutting        distance Rc and said final clearance distance Rd, satisfying the        relation:

0<Δp<Δd, with Δp=|Rc−Rp| and Δd=|Rc−Rd|.

An advantage of such a cutting tool resides in the fact that for everyactive part, the radial cutting edge constitutes the only zone of theperipheral surface of the active part that reaches the cutting envelope.

According to a first variant of realisation that corresponds to acutting tool of the solid type, the clearance face extends from theradial cutting edge while getting closer to the longitudinal axis of thebody up to a final clearance distance. According to a second variant ofrealisation that corresponds to a cutting tool of the shell type, theclearance face similarly extends from the radial cutting edge whiledeparting from the longitudinal axis of the body up to a final clearancedistance.

For the two variants of realisation, the control face extends at adistance that lies between the cutting distance and the final clearancedistance. It follows that chips that have not been eliminated into theflute preceding the radial cutting edge in the direction of rotation ofthe cutting tool, can be conveyed along the clearance face and thenalong the control face up to the following flute, where they can remainprior to being eliminated. The danger of chips stuck in front of activeparts is strongly reduced if not suppressed. The control face moreoverallows one to measure or impose with precision a minimum distance ofpenetration of the radial cutting edge into the workpiece. Lastly, thefact that the penetration control distance has a value between thecutting distance and the final clearance distance, allows one tosignificantly reduce the vibrations during cutting.

According to the first variant of realisation, the body is a cylindricalor conical or rounded-shaped body, with a radius that coincides with thecutting distance.

According to a characteristic of this first variant of realisation, thefree end of said body comprises protruding front edges where each frontedge substantially extends up to the longitudinal median plane that isperpendicular to it, and wherein at least one of said front edgesextends beyond said longitudinal median plane that is perpendicular toit. An advantage of this characteristic resides in the fact that thefree end of the cutting tool is given an additional function. With the“solid-type” cutting tools known until now, the central part of the freeend only serves to pierce the material to be machined. According to theinvention, when at least one front edge extends beyond the longitudinalmedian plane that is perpendicular to it, the central part of the freeend becomes a zone that not only pierces but also cuts. According to anadditional characteristic of this first variant of realisation, each ofthese front edges is situated in the longitudinal extension of a flutewall on which a radial cutting edge is resting.

According to the second variant of realisation, the body is an annularbody with a cylindrical or conical or rounded shape, and having an innerradius that coincides with the cutting distance.

Particular embodiments of the cutting tool according to the first aspectof the invention are defined in the appended claims 2 to 5, 7 to 13, 16,17, and 19 to 24.

According to a second aspect, the invention relates to methods applyinga cutting tool according to the first aspect of the invention, and inparticular:

-   -   a method of preparing a root canal during an endodontic        treatment that applies a cutting tool according to the first        variant of the first aspect of the invention,    -   a method of machining of a setting claw in the field of jewelery        that applies a cutting tool according to the second variant of        the first aspect of the invention.

The invention will be better understood when reading the followingdetailed description of particular embodiments of the cutting tool thatare provided as an illustration and are by no means limiting, whilereferring to the annexed drawings where:

FIG. 1 represents in perspective a “solid-type” milling cutter havingtwo flutes and two active parts;

FIG. 2 represents a transverse section of the cutting tool of FIG. 1;

FIGS. 3 and 4 are analogues of FIG. 2 illustrating the size range of thecutting tool's core, as well as the volume range of the flutes;

FIGS. 5 and 6 are analogues of FIG. 2 illustrating the range of valuesof the angle of attack of the cutting tool's radial cutting edge;

FIGS. 7 and 8 are analogues of FIG. 2 illustrating the range of valuesof the cutting tool's penetration control distance;

FIG. 9 is an analogue of FIG. 2 illustrating a geometrical variant ofthe control face;

FIG. 10 represents the free end of the cutting tool in a front view;

FIGS. 11, 12 and 13 are analogues of FIG. 2 for cutting tools having oneflute and one active part, three flutes and three active parts, or fourflutes and four active parts, respectively;

FIG. 14 represents a “shell-type” cutting tool having two flutes and twoactive parts, in a transverse section;

FIG. 15 illustrates an alternative form of realisation of the cuttingtool of FIG. 14;

FIGS. 16 and 17 are analogues of FIG. 15 illustrating the range ofvalues of the cutting tool's angle of attack;

FIGS. 18 and 19 are analogues of FIG. 15 illustrating the range ofvalues of the cutting tool's angular clearance length;

FIGS. 20 and 21 are analogues of FIG. 15 illustrating the range ofvalues of the angular control length as well as the range of flutevolumes of the cutting tool;

FIGS. 22 and 23 are analogues of FIG. 15 illustrating the range ofvalues of the cutting tool's control distance.

First a solid-type milling cutter will be described as cutting tool 10while referring to FIGS. 1 to 13. FIG. 1 represents in perspective acutting tool 10 with a body 12 assembled on a shank 13 integral with adrive shaft 3. Body 12 is a cylindrical or conical body or a body havinga rounded form, of revolution about a longitudinal axis 14. By roundedform, a shape is understood that in longitudinal section has an envelopeof non-rectilinear profile. Such a rounded form could for example be aspherical, pear, barrel, or flame shape. Body 12 is provided with twostraight flutes 16 and two active parts 18 alternating with these flutes16. Body 12 terminates in a free end 90 that will be described in detaillater.

A transverse section of the cutting tool 10 of FIG. 1 is represented inFIG. 2. This transverse section has central symmetry.

Each flute 16 is delimited by two walls 162, 164, both flat and mutuallyperpendicular so that the bottom 166 of the flute 16 defines a rightangle.

Core 11 of body 12 is defined as the central part of the body that isinside a cylinder or cone or rounded form centred on the longitudinalaxis 14, and delimited by the bottoms 166 of flutes 16. This core 11 ofbody 12 has a diameter indicated by letter A in FIG. 2. Diameter A is apercentage of the diameter of body 12 comprised between 0% and 95% ofthat diameter, preferably between 5% and 30%, and even more preferablybetween 10% and 20%.

FIGS. 3 and 4 both represent a transverse section of a cutting tool 10analogous to that of FIG. 2, illustrating the size range of core 11 ofbody 12 as well as the volume range of the flutes 16. FIG. 3 shows themaximum value that can be attained by core 11 of cutting tool 10, andthe minimum value of the volume of the flutes 16, while FIG. 4 shows theminimum value that can be attained by core 11 of cutting tool 10, andthe maximum value of the volume of the flutes 16.

Returning to FIG. 2, it appears that the peripheral surface of eachactive part 18 comprises in succession: a radial cutting edge 20, aclearance face 30, and a control face 40, as well as a transition face50 extending between the clearance face 30 and the control face 40.

The radial cutting edge 20 is at a distance Rc, so-called cuttingdistance, from the longitudinal axis 14. It defines a cylindrical orconical or rounded cutting envelope 22 which has a radius equal to thecutting distance Rc and which is represented in FIG. 2 by a circle inbroken lines. The cutting distance Rc coincides with radius Rf of body12.

The radial cutting edge 20 rests on one of the walls of flute 16, moreprecisely on wall 162 which precedes it in the direction of rotation ofcutting tool 10 that is indicated by arrow 100 in the figures.

When this wall 162 is borne by a radius Rf of body 12 as shown in FIG.2, then the radial cutting edge 20 has an angle of attack β that issubstantially zero. When this wall 162 departs from a radius of body 12in the direction from the radial cutting edge 20 toward the active part18 as represented in FIG. 5, then the radial cutting edge 20 has anegative angle of attack β. When this wall 162 departs from a radius ofbody 12 in the direction from the radial cutting edge 20 toward flute 16as represented in FIG. 6, then the radial cutting edge 20 has a positiveangle of attack β.

This angle of attack β is comprised between −45° and 45°, preferablybetween −20° and 20°, and even more preferably between −10° and 10°.

According to the invention it is preferred that the angle of attack β benegative, of by default zero, so that cutting tool 10 will showcommensurate aggressiveness of cutting.

Coming back to FIG. 2, the clearance face 30 extends from the radialcutting edge 20 in the direction opposite to that of rotation 100 of thecutting tool 10. This clearance face 30 is a substantially flat facedefined by a clearance angle α and by an angular clearance length δd. Itis at a distance from the longitudinal axis 14 that varies between thecutting distance Rc at its end abutting the radial cutting edge 20, anda final clearance distance Rd at its opposite end.

The clearance angle α is the angle formed between this clearance face 30and the plane that is tangent to the cutting envelope 22, and having theradial cutting edge 20 as its apex. This clearance angle α is comprisedbetween 0° and 45°, preferably between 5° and 30° and even morepreferably between 10° and 20°.

The angular clearance length δd is the angle of the sector that iscentred on the longitudinal axis 14 and delimits the clearance face 30.This angular clearance length δd is comprised between 5° and 160°,preferably between 6° and 50° and even more preferably between 7° and10°.

The angular length δd of this clearance face 30 depends on the grindingwheel used to machine the cutting tool 10, and on the diameter and shapeof said cutting tool 10. The final clearance distance Rd is a functionof the clearance angle α and of the angular clearance length δd.

Since the cutting tool 10 is a solid-type milling cutter, and has atransverse section inscribed into a disc, then the final clearancedistance Rd is smaller than the cutting distance Rc. It follows that theabsolute difference Δd between the cutting distance Rc and the finalclearance distance Rd represents the radial distance between the cuttingenvelope 22 and the peripheral surface of the active part 18 at the endof the clearance face 30. This absolute difference Δd is comprisedbetween 0.03 mm and 0.3 mm.

A transition face 50 that will be described in greater detail in thefollowing, extends from the clearance face 30, still in the directionopposite to that of rotation 100 of cutting tool 10.

The control face 40 that is defined by an angular penetration controllength δp, and is at a distance Rp, so-called penetration controldistance, from the longitudinal axis 14, extends from the transitionface 50, still in the direction opposite to that of rotation 100 ofcutting tool 10.

The angular penetration control length δp is the angle of the sectorcentred on the longitudinal axis 14 that delimits the control face 40.This angular penetration control length δp is comprised between 0° and100°, preferably between 5° and 60°, and even more preferably between10° and 30°.

The angular length δp of this control face 40 depends on the cuttingcapacity, on the size of the grinding wheel used to machine the cuttingtool 10, and on the dimensions of said cutting tool 10.

A first form of realisation of said control face 40 for which thepenetration control distance Rp is constant so that said control face 40exhibits a profile of substantially a circular arc in a plane transverseto said longitudinal axis 14, is illustrated in FIG. 2.

The absolute difference Δp between the cutting distance Rc and thepenetration control distance Rp represents the radial distance betweenthe cutting envelope 22 and the peripheral surface of the active part 18along the control face 40. This absolute difference Δp is comprisedbetween 0.03 mm and 0.3 mm.

FIGS. 7 and 8 both represent a transverse section of a cutting tool 10analogous to that of FIG. 2 and illustrate the range of values of thisdifference Δp. FIG. 7 shows the minimum value of this difference Δp,while FIG. 8 shows the maximum value of this difference Δp.

FIG. 9 illustrates a second form of realisation of said control face 40that is a substantially flat face for which the penetration controldistance Rp is not constant, so that said control face 40 in a planetransverse to said longitudinal axis 14 has a substantially rectilinearprofile. Preferably this rectilinear profile substantially correspondsto the chord of the circular-arc profile of the variant illustrated inFIG. 2.

According to a characteristic of the first variant of realisation of thecutting tool 10 the cutting distance Rc, the final clearance distance Rdand the penetration control distance Rp satisfy the relation: Rd<Rp<Rc.

More particularly, the difference between the cutting distance Rc andthe penetration control distance Rp is greater than zero and smallerthan the difference between the cutting distance Rc and the finalclearance distance Rd, which translates to the relation: 0<Rc−Rp<Rc−Rd.

Said otherwise, the absolute difference between the cutting distance Rcand the penetration control distance Rp is different from zero, andsmaller than the absolute difference between the cutting distance Rc andthe final clearance distance Rd, which translates to the relation:

0<Δp<Δd, with Δp=|Rc−Rp| and Δd=|Rc−Rd|.

Returning now to FIG. 2, the transition face 50 will be described. Thistransition face 50 is defined by an angular transition length δt, and isat a distance Rt, so-called transition distance, from the longitudinalaxis 14.

The angular transition length δt is the angle of the sector centred onthe longitudinal axis 14 that delimits the transition face 50. It iscomprised between 0° and 150°, preferably between 30° and 120°, and evenmore preferably between 60° and 90°.

The transition face 50 serves to link the clearance face 30 and thecontrol face 40. Preferably, the transition face 50 has a generallyconvex contour. In the example illustrated in FIG. 2, the transitionface 50 has, in transverse section, a contour consisting of a centralpart in the shape of a circular arc substantially concentric with thecutting envelope 22, and of two terminal parts situated to both sides ofthe central part. These two terminal parts are more or less long, andprogressively link the central part with the clearance face 30 and thecontrol face 40 that are situated to both sides of this transition face50.

The value of the transition distance Rt has no particular significance,since the only function of transition face 50 is that of linking theclearance face 30 and the control face 40. It is only important that thepenetration control distance Rp remain larger than this transitiondistance Rt, and satisfy the relation: Rt<Rp<Rc. Said otherwise, theabsolute difference Δp between the cutting distance Rc and thepenetration control distance Rp remains smaller than the absolutedifference Δt between the cutting distance Rc and the transitiondistance Rt, satisfying the relation:

0<Δp<Δt, with Δp=|Rc−Rp| and Δt=|Rc−Rt|.

An advantage of this arrangement (Δp<Δt) resides in the fact that thechips that might not have been eliminated into the flute 16 precedingthe radial cutting edge 20 may easily be conveyed between the clearanceface 30 and the control face 40 without being retained or slowed down inwhatever way at the transition face 50.

The free end 90 of the cutting tool 10 of FIG. 1 is illustrated in FIG.10 in a front view. The two radial cutting edges 20 define the cuttingenvelope 22. The clearance face 30 is followed by a transition face 50that in turn is followed by a control face 40. Each flute 16 isdelimited by two walls 162, 164 mutually substantially perpendicular andmeeting at the bottom 166 of flute 16. Each radial cutting edge 20 restson wall 162 of the flute 16 preceding it in the direction of rotation100 of cutting tool 10. Each of these walls 162 is extended forward,along the direction of the longitudinal axis 14, by a front edge 92,92′. A longitudinal median plane perpendicular to the two edges 92, 92′is indicated by letter P. Considering the upper part of FIG. 10, thefront edge 92 substantially extends up to the longitudinal median planeP. Considering the lower part of FIG. 10, the other front edge 92′extends beyond this longitudinal median plane P. It follows that asubstantially central zone 94 of free end 90 of the cutting tool 10exists that is a zone of overlap between these two front edges 92, 92′.In the example illustrated, this overlap zone 94 is on only one side(the right-hand side in FIG. 10) of the longitudinal median plane P. Ina variant, the overlap zone 94 could be on both sides of thislongitudinal median plane P, while the free end 90 would have its twoedges 92, 92′ extending beyond the longitudinal median plane P, but theconfiguration of FIG. 10 is preferred.

It appears that the cutting will be more efficient the larger the numberof front edges extending beyond the longitudinal median plane that isperpendicular to them. However, if the number of such front edges is toolarge, the central part of the free end becomes fragile, which may causeone or several edges to break. This is why it is preferable to limit thenumber of edges concerned. For instance, when the free end of thecutting tool has exactly two front edges, it is preferable that only oneof these two edges extend beyond the longitudinal median planeperpendicular to it. This is the example illustrated in FIG. 10.

FIGS. 11, 12, and 13 illustrate alternative embodiments of the cuttingtool 82, 84, 86 that differ from the cutting tool 10 illustrated in FIG.2 by the number of flutes 16 and active parts 18 that they have. Thecutting tool 82 illustrated in FIG. 11 has one flute 16 and one activepart 18. In this case the angular penetration control length δp iscomprised between 0 and 300°. The cutting tool 84 illustrated in FIG. 12has three flutes 16 and three active parts 18. The cutting tool 86illustrated in FIG. 13 has four flutes 16 and four active parts 18.Their other characteristics are analogous to those described whilereferring to FIGS. 1 to 10.

A cutting tool 10 corresponding to the first variant of realisation thathas just been described while referring to FIGS. 1 to 13 can be appliedin a method of preparing a root canal during dental treatment. Such acutting tool 10 is preferably made of tungsten carbide, martensiticstainless steel, or carbon steel.

A shell-type milling cutter will now be described as a cutting tool 110while referring to FIGS. 14 to 23.

FIG. 14 represents a transverse section of a cutting tool 110 includinga hemispherical calotte 111 that is extended by an annular body 112 thatis cylindrical or conical, or of a rounded form, of revolution about alongitudinal axis 114. This transverse section has central symmetry.Body 112 is provided with two helical flutes 116 and two helical activeparts 118 alternating with these flutes 116. It has an inner radius Riand a thickness Ep.

Still in FIG. 14, the peripheral surface of each active part 118comprises in succession: a radial cutting edge 120, a clearance face130, and a control face 140, as well as a transition face 150 extendingbetween the clearance face 130 and the control face 140.

Referring to FIG. 15, a transverse section of an alternative form ofrealisation of the cutting tool of the type of a shell-type millingcutter is represented, where the transition face 150 is reduced to apurely radial face.

The radial cutting edge 120 is at a distance Rc, so-called cuttingdistance, from the longitudinal axis 114. It defines a cylindrical orconical or rounded cutting envelope 122, of annular shape, representedby a circle in broken lines in FIGS. 14 and 15.

The radial cutting edge 120 rests on one of the walls of flute 116, moreprecisely on wall 1162 which precedes it in the direction of rotation ofcutting tool 110 that is indicated by arrow 100 in the figures.

When this wall 1162 is borne by a radius of body 112 as shown in FIGS.14 and 15, then the radial cutting edge 120 has an angle of attack βthat is substantially zero. When this wall 1162 departs from a radius ofbody 112 in the direction from the radial cutting edge 120 toward theactive part 118 as represented in FIG. 16, then the radial cutting edge120 has a positive angle of attack β. When this wall 1162 departs from aradius of body 112 in the direction from the radial cutting edge 120toward flute 116 as represented in FIG. 17, then the radial cutting edge120 has a negative angle of attack β.

This angle of attack β is comprised between −45° and 45°, preferablybetween −20° and 20°, and even more preferably between −10° and 10°.

According to the invention it is preferred that the angle of attack β benegative, of by default zero, so that cutting tool 110 will showcommensurate aggressiveness of cutting.

Coming back to FIGS. 14 and 15, the clearance face 130 extends from theradial cutting edge 120 in the direction opposite to that of rotation ofcutting tool 110. This clearance face 130 is a substantially flat facedefined by a clearance angle α and by an angular clearance length δd. Itis at a distance from the longitudinal axis 114 that varies between thecutting distance Rc at its end abutting the radial cutting edge 120 anda final clearance distance Rd at its opposite end.

The clearance angle α is the angle formed between this clearance face130 and the plane that is tangent to the cutting envelope 122, andhaving the radial cutting edge 120 as its apex. This clearance angle αis comprised between 0° and 30°, preferably between 5° and 25° and evenmore preferably between 10° and 20°.

The angular clearance length δd is the angle of the sector that iscentred on the longitudinal axis 114 and delimits the clearance face130. This angular clearance length δd is comprised between 10° and 90°,preferably between 20° and 60° and even more preferably between 30° and45°.

FIGS. 18 and 19 both represent a transverse section of a cutting tool110 analogous to that of FIG. 15, illustrating the range of values ofthe angular clearance length δd. FIG. 18 shows the maximum value thatcan be attained by the angular clearance length δd, while FIG. 19 showsthe minimum value that can be attained by the angular clearance lengthδd.

The angular length δd of this clearance face 130 depends on the size ofthe milling cutter used to machine the cutting tool 110, and on thediameter of said cutting tool 110. The final clearance distance Rd is afunction of the clearance angle α and of the angular clearance lengthδd.

The final clearance distance Rd is larger than the cutting distance Rc,since the cutting tool 110 is a shell-type milling cutter and has atransverse section inscribed into a ring. It follows that the absolutedifference Δd between the cutting distance Rc and the final clearancedistance Rd represents the radial distance between the cutting envelope122 and the peripheral surface of the active part 118 along thisclearance face 130. This absolute difference Δd is a percentage of theouter radius that is defined as the sum of inner radius Ri and thicknessEp of the annular body 112. The absolute difference Δd is comprisedbetween 2% and 15% of the outer radius, and preferably substantiallyequal to 7% of said outer radius.

A transition face 150 that will be described in greater detail in thefollowing while referring to both FIGS. 14 and 15 extends from theclearance face 130, still in the direction opposite to that of rotation100 of the cutting tool 110.

The control face 140 that is defined by an angular penetration controllength δp, and that is at a distance Rp, so-called penetration controldistance, from the longitudinal axis 114, extends from the transitionface 150, still in the direction opposite to that of rotation 100 of thecutting tool 110.

The angular penetration control length δp is the angle of the sectorcentred on the longitudinal axis 114 that delimits the control face 140.This angular penetration control length δp is comprised between 60° and140°, preferably between 75° and 130° and even more preferably between90° and 120°.

The angular control length δp of this control face 140 depends on thecutting capacity, on the size of the grinding wheel or milling cutterused to machine the cutting tool 110, and on the dimensions of saidcutting tool 100.

FIGS. 20 and 21 both represent a transverse section of a cutting tool110 analogous to that of FIG. 15 illustrating the range of values ofsaid angular control length δp. FIG. 20 shows the maximum value that canbe attained by this angular penetration control length δp, while FIG. 21shows the minimum value that can be attained by the angular penetrationcontrol length δp.

In the example illustrated in FIGS. 14 to 23, the penetration controldistance Rp is constant, so that said control face 140 has a profilethat in a plane transverse to the longitudinal axis 114 is substantiallya circular arc.

The absolute difference Δp between the cutting distance Rc and thepenetration control distance Rp represents the radial distance betweenthe cutting envelope 122 and the peripheral surface of the active part118 along this control face 140. This absolute difference Δp iscomprised between 0.03 mm and 0.3 mm.

FIGS. 22 and 23 both represent a transverse section of a cutting tool110 analogous to that of FIG. 15 illustrating the range of values ofthis difference Δp. FIG. 22 shows the maximum value that can be attainedby this difference Δp, while FIG. 23 shows the minimum value that can beattained by this difference Δp.

According to a characteristic of the second variant of realisation ofthe cutting tool 110 the cutting distance Rc, the final clearancedistance Rd, and the penetration control distance Rp satisfy therelation: Rc<Rp<Rd.

More particularly, the difference between the penetration controldistance Rp and the cutting distance Rc is greater than zero and smallerthan the difference between the final clearance distance Rd and thecutting distance Rc, which translates to the relation: 0 <Rp−Rc<Rd−Rc.

Said otherwise, the absolute difference between the cutting distance Rcand the penetration control distance Rp is different from zero, andsmaller than the absolute difference between the cutting distance Rc andthe final clearance distance Rd, which translates to the relation:

0<Δp<Δd, with Δp=|Rc−Rp| and Δd=|Rc−Rd|.

Returning now to FIGS. 14 and 15, the transition face 150 will bebriefly described. This transition face 150 is defined by an angulartransition length δt and is at a distance Rt, so-called transitiondistance, from the longitudinal axis 114.

In the example illustrated in FIG. 14, the angular transition length δtis the angle of the sector centred on the longitudinal axis 114 thatdelimits the transition face 150. It is comprised between 0° and 150°,preferably between 30° and 120° and even more preferably between 60° and90°.

Preferably, the transition face 150 has a generally concave contour. Inthe example illustrated in FIG. 14, the transition face 150 has, intransverse section, a contour consisting of a central portion in theshape of a circular arc substantially concentric with the cuttingenvelope 122, a purely radial portion for linking to the clearance face130, and a substantially rectilinear portion for linking to the controlface 140.

In the example illustrated in FIG. 15 as well as in FIGS. 16 to 23, thetransition face 150 is purely radial, so that the angular transitionlength δt is zero, and the transition distance Rt varies between Rd andRp.

The function of transition face 150 is that of linking the clearanceface 130 and the control face 140. For this reason, the value of thetransition distance Rt has no particular significance. It is onlyimportant that the penetration control distance Rp remain smaller thanthis transition distance Rt, and satisfy the relation: Rc<Rp<Rt. Saidotherwise, the absolute difference Δp between the cutting distance Rcand the penetration control distance Rp remains smaller than theabsolute difference Δt between the cutting distance Rc and thetransition distance Rt, satisfying the relation:

0<Δp<Δt, with Δp=|Rc−Rp| and Δt=|Rc−Rt|.

Still referring to FIGS. 14 and 15, it appears that each flute 116 isdelimited by at least two flat walls 1162, 1164. Depending on the radialthickness of the active part 118 of cutting tool 110, each flute 116 mayeither be open toward the outside, as represented in the figures, orclosed by a bottom linking the two walls 1162 and 1164. FIGS. 20 and 21also illustrate the range of volumes of flutes 116. FIG. 20 shows theminimum value of the volume of flutes 116. Since the angle of attack βis substantially zero in this example, wall 1162 is substantiallyperpendicular to the cutting envelope 122. The other wall 1164 of theflutes 116 is not perpendicular to the cutting envelope 122, so thatthere always remains a minimum volume of the flutes 116 at which the twowalls 1162 and 1164 link up. FIG. 21 in turn shows the maximum value ofvolume of the flutes 116.

A cutting tool 110 corresponding to the second variant of realisationthat has just been described while referring to FIGS. 14 to 23 can beapplied in the field of jewelery in a method of machining a settingclaw. Such a cutting tool 110 is preferably made of carbon steel or ofmartensitic stainless steel.

In a way common to the two variants of realisation that have just beendescribed while referring to FIGS. 1 to 13 and 14 to 23, respectively,the active part 18, 118 of the cutting tool 10, 110 comprises insuccession: a radial cutting edge 20, 120 at a cutting distance Rc fromthe longitudinal axis 14, 114 of the cutting tool 10, 110, a clearanceface 30, 130 at a distance from the longitudinal axis 14, 114 thatvaries between the cutting distance Rc and a final clearance distanceRd, and a control face 40, 140 at a penetration control distance Rp fromthe longitudinal axis 14, 114, these distances Rc, Rd, Rp satisfying thefollowing relation: 0 <|Rc−Rp|<|Rc−Rd|.

Moreover, the active part 18, 118 of the cutting tool 10, 110additionally comprises a transition face 50, 150 that is at a variabledistance Rt from the longitudinal axis 14, 114. This distance Rt isvariable and comprised between Rp and Rd. It satisfies the relation: 0<|Rc−Rp|<|Rc−Rt|.

It is understood that the invention is not limited to the variants andforms of realisation that have been illustrated in the figures, andextends to alternatives in the capacity of one skilled in the art.

The cutting tools 10, 110 that have been shown as examples comprisebetween one and four flutes, and between one and four active parts. Theinvention also refers to cutting tools 10, 110 having flutes and activeparts numbering more than four.

The cutting tools 10, 110 that have been shown as examples comprisestraight flutes and straight active parts. One could contemplate flutesand active parts that are not straight but for instance helical.

The characteristic illustrated in FIG. 10 according to which each frontedge extends substantially up to the longitudinal median planeperpendicular to it, and at least one of said front edges extends beyondsaid longitudinal median plane perpendicular to it, can be generalisedto cutting tools 84 having three flutes and three active parts, tocutting tools 86 having four flutes and four active parts, and tocutting tools having even more flutes and active parts.

In a particular variant of realisation of a cutting tool 10 assolid-type milling cutter that is illustrated in FIGS. 1 to 13, theflutes 16 exhibit two walls 162, 164 that are mutually perpendicular.This geometry of the flutes 16 is not limiting. In particular, flutes 16could be formed by two walls 162, 164 delimiting an acute angle or anobtuse angle in transverse section. In a variant, these flutes 16 couldexhibit walls 162, 164 that are non-rectilinear, and/or a rounded bottom166.

1. Cutting tool (10, 82, 84, 86, 110) of a rotating type, in particulara milling cutter or borer, said cutting tool (10, 82, 84, 86, 110) beingprovided with a body (12, 112) having a longitudinal axis (14, 114) andat least one flute (16, 116) alternating with at least one active part(18, 118), characterised in that each active part (18, 118) has aperipheral surface comprising in succession: a radial cutting edge (20,120), a clearance face (30, 130), to favour the elimination of chips,and a control face (40, 140) to control the depth of penetration of thecutting, said control face opening into a flute (16, 116), and in thatsaid radial cutting edge (20, 120) defines a cutting envelope (22, 122)and is situated at a cutting distance (Rc) from said longitudinal axis(14, 114), said clearance face (30, 130) is defined by an angularclearance length (δd) and is situated at a distance from saidlongitudinal axis (14, 114) that varies between the cutting distance(Rc) and a final clearance distance (Rd), said control face (40, 140) isdefined by an angular penetration control length (δp) and is situated ata penetration control distance (Rp) from said longitudinal axis (14,114), and the absolute difference (Δp) between said cutting distance(Rc) and said penetration control distance (Rp) is larger than zero, andsmaller than the absolute difference (Δd) between said cutting distance(Rc) and said final clearance distance (Rd), satisfying the relation:0<Δp<Δd, with Δp=|Rc−Rp| and Δd=|Rc−Rd|.
 2. Cutting tool (10, 82, 84,86, 110) according to claim 1, wherein said radial cutting edge (20,120) is defined by an angle of attack (β) that is substantially zero. 3.Cutting tool (10, 82, 84, 86, 110) according to claim 1, wherein saidradial cutting edge (20, 120) is defined by an angle of attack (β) thatis negative.
 4. Cutting tool (10, 82, 84, 86, 110) according to claim 1,wherein said radial cutting edge (20, 120) is defined by an angle ofattack (β) that is positive.
 5. Cutting tool (10, 82, 84, 86, 110)according to claim 1, wherein said clearance face (30, 130) is asubstantially flat face.
 6. Cutting tool (10, 82, 84, 86) according toclaim 1, wherein said body (12) is a cylindrical or conical orrounded-shaped body, with a radius (Rf) that coincides with the cuttingdistance (Rc).
 7. Cutting tool (10, 82, 84, 86) according to claim 6,wherein said penetration control distance (Rp) is constant, so that saidcontrol face (40) in a plane transverse to said longitudinal axis (14)has a circular-arc profile.
 8. Cutting tool (10, 82, 84, 86) accordingto claim 6, wherein said penetration control distance (Rp) is linear, sothat said control face (40) in a plane transverse to said longitudinalaxis (14) has a rectilinear profile.
 9. Cutting tool (10, 82, 84, 86)according to claim 6, wherein said angular clearance length (δd) iscomprised between 5° and 160°.
 10. Cutting tool (10, 82, 84, 86)according to claim 6, wherein said absolute difference (Δd) between saidcutting distance (Rc) and said final clearance distance (Rd) iscomprised between 0.03 mm and 0.3 mm.
 11. Cutting tool (10, 82, 84, 86)according to claim 6, comprising at least two flutes (16) and at leasttwo active parts (18), and wherein said angular penetration controllength (δp) is comprised between 0° and 100°.
 12. Cutting tool (10, 82,84, 86) according to claim 6, comprising a single flute (16) and asingle active part (18), and wherein said angular penetration controllength (δp) is comprised between 0° and 300°.
 13. Cutting tool (10, 82,84, 86) according to claim 6, wherein the absolute difference (Δp)between said cutting distance (Rc) and said penetration control distance(Rp) is comprised between 0.03 mm and 0.3 mm.
 14. Cutting tool (10, 82,84, 86) according to claim 6, wherein the free end (90) of said body(12) comprises protruding front edges (92, 92′), wherein each front edge(92, 92′) extends substantially at least up to the longitudinal medianplane (P) that is perpendicular to it, and wherein at least one (92′) ofsaid front edges (92, 92′) extends beyond said longitudinal median plane(P) that is perpendicular to it.
 15. Cutting tool (10, 82, 84, 86)according to claim 14, wherein each of these front edges (92, 92′) issituated in the longitudinal extension of a wall (162) of a flute (16)on which a radial cutting edge (20) is resting.
 16. Cutting tool (10,82, 84, 86) according to claim 14, wherein said body comprises exactlytwo flutes and two active parts, and wherein said front edges (92, 92′)are numbering two and are substantially parallel.
 17. Cutting tool (10,82, 84, 86) according to claim 14, wherein just one (92′) of said frontedges (92, 92′) extends beyond said longitudinal median plane (P). 18.Cutting tool (110) according to claim 1, wherein said body (112) is anannular body with a cylindrical or conical or rounded shape, and havingan inner radius (Ri) that coincides with said cutting distance (Rc). 19.Cutting tool (110) according to claim 18, wherein said penetrationcontrol distance (Rp) is constant, so that said control face (140) in aplane transverse to said longitudinal axis (114) has a circular-arcprofile.
 20. Cutting tool (110) according to claim 18, wherein saidangular clearance length (δd) is comprised between 10° and 90°. 21.Cutting tool (110) according to claim 18, wherein the absolutedifference (Δd) between said cutting distance (Rc) and said finalclearance distance (Rd) is comprised between 2% and 15% of an outerradius that is defined as the sum of the inner radius (Ri) and thethickness (Ep) of the annular body (112).
 22. Cutting tool (110)according to claim 18, wherein the angular penetration control length(δp) is comprised between 60° and 140°.
 23. Cutting tool (110) accordingto claim 18, wherein the absolute difference (Δp) between said cuttingdistance (Rc) and said penetration control distance (Rp) is comprisedbetween 0.03 mm and 0.3 mm.
 24. Cutting tool (10, 82, 84, 86, 110)according to claim 1, wherein the periphery of each active part (18,118) in addition comprises a transition face (50, 150) extending betweensaid clearance face (30, 130) and said control face (40, 140), saidtransition face (50, 150) being situated at a transition distance (Rt)from the longitudinal axis (14, 114), and wherein the absolutedifference (Δp) between the cutting distance (Rc) and the penetrationcontrol distance (Rp) is smaller than the absolute difference (Δt)between the cutting distance (Rc) and said transition distance (Rt),satisfying the relation:0<Δp<Δt, with Δp=|Rc−Rp| and Δt=|Rc−Rt|.
 25. Method of preparing a rootcanal for an endodontic treatment, characterised in that it applies acutting tool (10, 82, 84, 86) according to claim
 6. 26. Method ofmachining a setting claw in the field of jewelery, characterised in thatit applies a cutting tool (110) according to claim 18.